The present invention relates to a method of preparing ethylene glycol from cellulose, and more particularly to a reaction process of cellulose which comprises catalytic degradation and hydrogenation reactions.

Ethylene glycol is a liquid fuel, and also is an important feed for polyester synthesis. For example, ethylene glycol can be used for synthesizing polyethylene terephthalate (PET), and polyethylene naphthalate (PEN); ethylene glycol can also be used in antifreeze agents, lubricant, plasticizers, or surfactant etc. Thus, ethylene glycol has a variety of applications.

At present, the industrial process for producing ethylene glycol is consuming petroleum resources as the raw material, wherein the ethylene glycol is produced via oxidizing ethylene to form epoxyethane, and then hydrating it to obtain the ethylene glycol. (Literature 1: CUI Xiao-ming, the overview of the production development of ethylene glycol, Chemical Industry, 2007,25, (4), 15-21. Literature 2: Process for preparing ethanediol by catalyzing epoxyethane hydration, Patent No. CN1463960-A; Patent No. CN1204103-C). The conventional method for ethylene glycol production is based on the nonrenewable petroleum sources, and involving the oxidization or epoxidation process, which comprises complicated reaction steps, so that the procedure of preparing ethylene glycol is of low efficiency, containing high amount of undesired side products, consuming much energy, and causing serious pollution.

Therefore, finding renewable materials for producing ethylene glycol is able to reduce the dependence on the petroleum, so as to build an eco friendly manufacturing process. Currently, the researches of converting the biomass into ethylene glycol are mostly focusing on starch, glucose, sucrose, and sugar alcohols, such as hexitols, as the raw materials for the conversion therefrom. (Literature 3: Process for the preparation of lower polyhydric alcohols, Patent, No. US5107018. Literature 4: Preparation of lower polyhydric alcohols, Patent, No. US5210335). However, the above mentioned raw materials for the conversion of ethylene glycol are the currently basic food of human beings, so that using them for ethylene glycol production is facing the dilemma of mankind's survival and development. Cellulose is the largest renewable resource, having rich sources, such as the remaining straw from agricultural production or wastes from forestry, etc., which are low in cost for using as the raw material for the conversion of biomass. Using cellulose for synthesizing ethylene glycol can not only build up a new synthesis process to achieve low cost, but also obtain the high value product of the ethylene glycol. Furthermore, cellulose is unable to be digested by human beings, so that using cellulose as the raw material for ethylene glycol production will not affect food security and not reduce the food production for the mankind. In addition, the cellulose is formed by the condensation of glycosidic bond of glucose units containing a large number of hydroxyls. Those hydroxyls are fully preserved during the process of cellulose converting into ethylene glycol, which makes the conversion process have a very high atom economy. Therefore, the process of converting cellulose into ethylene glycol has significant advantages over most of the existing processes of making ethylene glycol.

Though there are numbers of advantages of producing polyols from cellulose, cellulose contains a large amount of intermolecular and intramolecular hydrogen bonds, so that the structure of cellulose is very robust. Therefore, cellulose is usually first hydrolyzed to reducing sugar by acids, and then the obtained glucose is further converted for other uses. The whole process is not only complicated, but also generates environmental pollution issues. (Literature 4: Two stage hydrogenolysis of carbohydrate to glycols using sulfide modified ruthenium catalyst in second stage, Patent, No. US4476331). The present invention provides a reaction process, which is using water, the most environmental friendly solvent, as the reaction medium, has no need of adding acid or base, and is able to be completed via one step to accomplish the high yield of ethylene glycol from cellulose.

Direct conversion of cellulose into ethylene glycol by hydrogenation is also taught by Na Ji et al., Angew. Chem. Int. Ed., 47 (44), 8510-8511 (2008). Their favoured catalyst is nickel-promoted tungsten carbide on activated carbon, prepared by hydrogenating a tungsten precursor compound in the presence of nickel.

An object of the present invention is to provide a method of preparing ethylene glycol from cellulose, which comprises one step of catalytic hydrogenation of cellulose to ethylene glycol with high yield and high selectivity thereof.

Accordingly, in order to accomplish the above objective, the present invention provides a method of preparing ethylene glycol from cellulose, wherein cellulose is used as feed. A catalyst is added to cellulose, wherein the catalyst comprises two sorts of active components, ascribed to a first active group and a second active group. A first active component of the first active group is one or more metals selected from the transition metals of group 8, 9, or 10, consisting of iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, and platinum. A second active component of the second active group is one or more materials selected from the group consisting of metallic molybdenum, metallic tungsten, molybdenum carbides, molybdenum nitrides, molybdenum phosphide, tungsten carbides, tungsten nitrides, and tungsten phosphide. The reaction is conducted in a sealed batch reactor, wherein the reactants are stirred therewith. The hydrogen filled in the reactor at room temperature has an initial pressure of 1 to 12MPa, the reacting temperature is 120-300°C, and the reacting time is no less than 5 minutes. The weight ratio of the second active component to the first active component is in the range of 0.02 to 1600. If the second active component is tungsten carbide, the first and second active components are mechanically mixed.

The active components may be supported on one or more compositions selected from the group consisting of active carbon, aluminum oxide, silica, zirconia, zinc oxide, and titanium dioxide. The metal loading of the first active component may be about 0.05-50 wt% , and the metal loading of the second active component may be about 1-80 wt%. Or, the catalysts are metallic skeletal catalysts without supports, such as Raney nickel, wherein the catalyst framework is made of the active components.

The mass ratio of the cellulose to water may be 1:200-1:4. The mass ratio of the cellulose to catalyst may be 1:1-30:1.

The reactions of each of the embodiments of the present invention are conducted in the high pressure reactor. The reaction can be conducted in a reactor with a better optimized design to achieve the better mass transfer among the cellulose, hydrogen, and catalyst to obtain a better reaction result.

The present invention has the following advantages.

1. 1. Use of cellulose as the feed, wherein cellulose has the largest production among the biomass in the natural resources, so that cellulose has very wide sources, such as from wood, cotton, remaining straw from the agricultural production, so as to minimize material and manufacturing cost. Currently, most industries use ethylene obtained from petroleum as the raw material for synthesizing ethylene glycol. The method of the present invention consumes no fossil energy resources, but uses cellulose of renewable resources, so as to meet the requirement of sustainable development.
2. 2. Compared to other processes using biomass as the feed materials for synthesizing ethylene glycol, such as using starch, glucose, and fructose as the feed materials for converting into ethylene glycol, the present invention uses cellulose, which is not a source of food of human beings, so that the present invention minimizes the concern of the impact of food safety to human beings.
3. 3. The method is simple, with no requirement of acid hydrolyzing the cellulose, so that the process is able to be completed via one-step conversion of cellulose to accomplish the high yield of ethylene glycol.
4. 4. After the cellulose is catalyzed for degradation thereof, the hydroxyls are fully reserved during the process of cellulose conversion into ethylene glycol, which makes the conversion process have a very high atom economy.
5. 5. The reaction is performed under hydrothermal conditions, wherein the cellulose conversion comprising reactions of catalytic degradation and hydrogenation is environmentally friendly. Water is used as the reacting medium, wherein no inorganic acid or base is required to be added in the reaction, so that the method of the present invention overcomes the pollution from the conventional degradation process of cellulose, so as to minimize environmental pollution.
6. 6. The reacting process has high yield and high selectivity of the target product, wherein the ethylene glycol yield may be about 70%, so that the method has great potential of applications in the future.

To sum up, the present invention provides a method for producing ethylene glycol from cellulose with high yield and high selectivity. Compared to the existing process using ethylene as the feedstock for synthesizing ethylene glycol, the process of the present invention using renewable resource as feeds is environmental friendly and has high atom economy.

An active carbon support was impregnated with ammonium metatungstate solution (0.4 g/ml of mass concentration), and then dried at 120°C for 12 hours. The dried sample was reduced at 700°C in hydrogen flow for one hour. A metallic tungsten catalyst was obtained (30 wt% tungsten loading).

The above tungsten catalyst was soaked with nickel nitrate solution, and then dried at 120°C. The derived sample was reduced at 400°C in a hydrogen flow for 2 hours to obtain a Ni-W/AC catalyst (15%Ni-25%W).

A silica support was impregnated with ammonium metatungstate solution (0.2 g/ml of mass concentration), and then dried at 120°C for 12 hours. The derived sample was reduced at 700°C for one hour in a hydrogen flow. W/SiO₂ (15 wt% tungsten loading) was obtained. The W/SiO₂ was impregnated with H₂PtCl₄ solution and dried at 120°C. Then, the dried sample was reduced at 350 °C for 2 hours in a hydrogen flow. The obtained catalyst was denoted as Pt-W/SiO₂ (0.5%Pt-15%W).

Active carbon support was impregnated with ammonium metatungstate solution (0.4 g/ml of mass concentration), and then dried at 120°C for 12 hours. The dried sample was reduced at 800°C for one hour in a hydrogen flow for carbothermal reaction to obtain a tungsten carbide catalyst W₂C/AC (30 wt% tungsten loading).

Active carbon was impregnated with ammonium metatungstate solution (0.2 g/ml of mass concentration), and then dried at 120°C for 12 hours. The dried sample was heated at 700°C for one hour in an NH₃ flow to obtain W₂N/AC containing 15 wt% of tungsten.

Active carbon was impregnated with mixed solutions of ammonium molybdate and nickel nitrate (Mo/Ni mass ration 1:1, mass concentration of ammonium molybdate 0.2 g/ml), and then dried at 120°C for 12 hours. The dried sample was heated at 700°C for one hour in an NH₃ flow to obtain Ni-W₂N /AC catalyst (15 wt% Ni-15 wt%W).

Active carbon was impregnated with ammonium molybdate solution (0.3 g/ml of mass concentration), and then dried at 120°C for 12 hours. The dried sample was heated at 700°C for one hour in an NH₃ flow to obtain Mo₂N/AC catalyst containing 15 wt% of Mo.

Active carbon was impregnated with mixed solutions of ammonium molybdate and nickel nitrate (Mo/Ni mass ratio of 1:1, mass concentration of ammonium molybdate 0.27 g/ml), and then dried at 120°C for 12 hours. The dried sample was heated at 700°C for one hour in an NH₃ flow to obtain catalyst Ni-Mo₂N /AC (15 wt% Ni-15 wt%Mo).

A TiO₂ support was impregnated with mixed solutions of ammonium molybdate and diammonium phosphate (Mo/P mole ratio 1:1.2), and then dried at 120°C for 12 hours. The dried sample was reduced at 650°C for 2 hours in a hydrogen flow to obtain a MoP/TiO₂ catalyst, which contains 16 wt% of Mo.

A TiO₂ support was impregnated with mixed solutions of ammonium molybdate, diammonium phosphate, and ruthenium trichloride (Mo/P mole ratio 1:1.2, and Mo/Ru weight ratio 8:1), and then dried at 120°C for 12 hours. The dried sample was reduced at 650°C for 2 hours in a hydrogen flow to obtain a Ru-MoP/TiO₂ catalyst, which contains 16 wt% of Mo and 2 wt% of Ru.

Catalytic conversion of cellulose was carried out in a sealed and high pressure reactor (200 ml) typically at 5 MPa H₂ pressure (measured at room temperature) and 240°C for 30 minutes. For each reaction, 1.0 g cellulose, 0.3 g catalyst and 100 ml water were put into the reactor and stirred. After the reaction, the liquid-phase products were analyzed by high-performance liquid chromatography (HPLC) and refractive index detector (RI). Cellulose conversions were determined by the change of cellulose weight before and after the reaction. The yield of polyols was calculated by the equation: yield (%) = (weight of polyol in the products)/(weight of cellulose put into the reactor) x 100%. The production yield rate only calculates the target products, which are ethylene glycol and hexitols (including sorbitol and mannitol). Other liquid products comprising propylene glycol, erythritol, ethanol and unknown components, and gas products, such as CO₂, CH₄ and C₂H₆, are not included in the yield.

Example 12: The results of catalytic conversion of cellulose over various metal and bimetallic catalysts (Table 1). The reacting conditions are the same as the above example 11. Catalyst Cellulose Conversion % Ethylene Glycol yield % Hexahydric alcohol yield % Others Yield % W/AC(30% W) 100 5 2 93 Ni-W/AC (15%Ni-25%W) 100 69 7 24 Pt-W/AC (0.5%Pt-75%W) 100 68 12 20 Pt-W/AC (0.5%Pt-15%W) 100 60 8 32 Ru-W/AC (0.5%Ru-15%W) 100 57 12 31 Mo-Ni/Al₂O₃ (15%Mo-15%Ni) 67 34 3 30 Pt/AC(1%Pt) 62 9 7 46 Ni/AC(20%Ni) 71 11 6 54 Ru/AC(2%Ru) 55 12 10 33

As can be seen from the Table 1, for the catalysts having single tungsten or the metals of group 8, 9, and 10, such as Ni, Pt, or and Ru, the ethylene glycol yields are relatively lower. However, when the bimetallic catalyst comprises catalytic hydrogenating component and tungsten, the yield of ethylene glycol is significantly increased, so that the bimetallic catalyst shows the high catalytic performance thereof. For example, the reaction applying the Ni-W catalyst is able to obtain the 69% yield of ethylene glycol.

Example 13: Table 2 shows the results of the cellulose conversion over molybdenum carbide catalysts, wherein the reacting conditions are the same as the example 11 described above. Catalyst Cellulose Conversion % Ethylene Glycol yield % Hexahydric alcohol yield % Others Yield % Mo₂C/AC(30%Mo) 45 5 2 38 Pt-Mo₂C/AC(2%Pt-30%Mo) 48 32 3 13

As can be seen from the results in Table 2, when the catalyst comprises the hydrogenating active components of Pt and the molybdenum carbide, the ethylene glycol has a yield significantly higher than that of using the molybdenum carbide catalyst only.

Example 14: Table 3 shows the results of the cellulose conversion over the nitrides catalysts and phosphide catalysts, wherein the reacting conditions are the same as the example 11. Catalyst Cellulose Conversion % Ethylene Glycol yield % Hexahydric alcohol yield % Others Yield % W₂N/AC(15%W) 95 12 8 75 W₂N-Ni/AC (15%W+15%Ni) 100 54 12 34 Mo₂N/AC(15% Mo) 65 6 3 56 Mo₂N-Ni/AC (15% Mo -15%Ni) 84 48 6 50 MoP/TiO₂(16%Mo) 69 4 2 63 MoP-Ru/TiO₂ (16%Mo-2% Ru) 76 31 9 26

Accordingly, when the molybdenum nitride, phosphide, and tungsten nitride catalysts contain group (8, 9, 10) metals, higher yields of ethylene glycol can be obtained.

Example 15: Table 4 shows the results of the cellulose conversion over the combined catalysts. The catalyst of tungsten carbide, metallic tungsten, or metallic molybdenum was physically mixed with the metallic catalysts of group (8, 9, 10) at weight ratio of 1 to 1, and tested in the reaction. The results of cellulose conversion are shown in Table 4. The reacting conditions are the same as example 11. Catalyst Cellulose Conversion % Ethylene Glycol yield % Hexahydric alcohol yield % Others Yield % W/AC(60%W) + Pt/AC(1%Pt) 100 55 6 39 W/AC(60%W) 100 3 2 95 Pt/AC(1%Pt) 62 9 7 46 W₂C/AC(30%W) + Ru/ SiO₂ (5%Ru) 100 46 8 46 Ru/SiO₂(5%Ru) 75 12 10 53 W₂C/AC(30%W) 95 18 5 72 W₂C/AC(30%W) + Ni/AC(20%Ni) 100 43 2 56 Ni/AC(20%Ni) 65 13 8 44 Raney Ni + W/AC(30%W) 100 53 7 39 Raney Ni 25 4 1 20 Mo/Al₂O₃ (10%Mo + Pt/ZrO₂(3%Pt) 72 32 6 34

As can be seen from the result shown in the Table 4, when the tungsten carbide, metallic tungsten, and molybdenum catalysts were mechanically mixed with the metallic catalysts of the group (8, 9, 10), ethylene glycol was obtained at higher yields compared with the catalysts having single active component. The combination of a skeletal catalyst such as Ni sponge and W can also lead a high yield of ethylene glycol.

Example 16: Table 5 shows the results of cellulose conversion over Ni-W/AC(15%Ni-25%W) as a function of reaction time. Except the reaction time is different, all other conditions are the same as example 11. Reaction time Cellulose Conversion % Ethylene Glycol yield % Hexahydric alcohol yield % Others Yield % 10 min 59 29 2 28 30 min 100 69 7 24 3 h 100 51 11 38 5 h 100 24 8 68 24 h 100 19 10 71

As can be seen from the results in Table 5, the nickel-tungsten carbide catalyst has good yields of ethylene glycol within a certain reaction time. The preferred reaction time is 30 minutes to 3 hours.

Example 17: Table 6 shows the results of cellulose conversion over Ni-W/AC(15%Ni-25%W) as a function of reaction temperatures. Except the reaction temperature is different, all other conditions are the same as example 11. Reaction temperature (°C) Cellulose Conversion % Ethylene Glycol yield % Hexahydric alcohol yield % Others Yield % 130 21 9 3 9 220 81 39 6 36 240 100 69 7 24 250 100 53 6 41 270 100 16 5 79

According to Table 6, the nickel-tungsten carbide catalyst added in the reaction system of the present invention for converting cellulose is able to obtain high yield of ethylene glycol. The preferred reaction temperature is in the range of 220∼250°C.

Example 18: The influence of reaction pressures on the cellulose conversion. Table 7 lists the results of cellulose conversion over Ni-W/AC(15%Ni-25%W) catalyst under different reaction pressures. Except the reaction pressures, all other reaction conditions are the same as example 11. Hydrogen pressure (MPa) Cellulose Conversion % Ethylene Glycol yield % Hexahydric alcohol yield % Others Yield % 2 33 8 4 21 3 89 36 5 48 5 100 69 7 24 6 100 56 8 36 7 100 53 6 41 12 100 33 4 63

According to the Table 7, the nickel-tungsten carbide catalyst in the reaction system of the present invention for converting cellulose is able to obtain high yield of the ethylene glycol under various hydrogen pressures. The preferred reaction pressure is between 3MPa to 7MPa.

It will thus be seen that the objects of the present invention have been fully and effectively accomplished. The embodiments have been shown and described for the purposes of illustrating the functional and structural principles of the present invention.